Engine systems including a high pressure fuel delivery system utilize a common rail (also known as a high pressure fuel rail, common rail, or accumulator) to accumulate and distribute fuel to fuel injectors at high-pressure while minimizing pressure fluctuations among the injectors. These systems allow for precise control of high-pressure injection of fuel by an engine control module (ECM) or an engine control unit (ECU) into the cylinders of an internal combustion engine at timing that is independent from the engine speed. The ECM/ECU receives an engine speed signal from a sensor and then, using its algorithms and look-up calibration tables stored in the ECM/ECU, controls the amount of injected fuel and the timing of injection, called “start of injection” (SOI), through electric or hydraulic actuators to maintain engine speed. Controlling the timing of the SOI of fuel into an engine cylinder is needed to control emissions and fuel economy of the engine system.
The timing of SOI is controlled electronically in most of today's modern engines. Advancing the SOI (i.e., injecting fuel when the piston is further away from top dead center (TDC)) results in higher in-cylinder pressure, temperature, and efficiency, but at the cost of higher emissions of nitrogen oxides (NOx) due to the higher temperatures. Retarding the SOI can causes incomplete combustion and result in higher particulate matter (PM) and unburned hydrocarbon (HC) emissions. The delay time from the point of a commanded (electric) SOI and hydraulic (actual) SOI is useful information for controlling performance, economy and emissions of such engine systems.